$\"\"$

The perimeter of the triangle $\"\"$ inches.

The length of the each side is $\"\"$ inches.

The perimeter P is the sum of the each side.

$\"\"$

$\"\"$ (Substitute 49 for P)

$\"\"$ (Add: $\"\"$ ) $\"\"$

$\"\"$ (Subtract 30 from each side)

$\"\"$ (Apply additive inverse property: $\"\"$ )

$\"\"$ (Apply additive identity property: $\"\"$ )

$\"\"$ (Subtract: $\"\"$ ) $\"\"$

The unknown side length is 19 inches.

The lengths of sides are 19, 12 and 18 inches. So, the triangle is Scalene triangle.